An electric coil generally includes axial winding layers, that is, each layer includes windings wound next to one another parallel to the coil axis. Most often, the coil includes many more windings in the axial direction than in the radial direction.
A disadvantage of such a coil is that two adjacent windings of two successive layers can be separated by a large number of turns, so that they are submitted to a voltage differential which is too high for the insulator of the windings, generally an enamel. Insulator layers thus have to be interposed between the layers of windings, which makes the coil more bulky and its fabrication more complex.
To avoid this disadvantage, in European patent application 0518737, it is provided to wind the windings in oblique layers. A coil obtained by this method has the disadvantage of being bulky since it has a trapezoidal cross-section which necessarily implies that the external diameter of the coil is larger, for a given number of windings, than that of a coil with a rectangular cross-section. The bulk of the coil is further increased by the fact that it includes a large number of crossing windings which hinder a contiguous disposition of the windings.
Due to the many winding crossings, this winding method is not applicable to conductors with a large diameter or a rectangular cross-section.